Electronic switching transient detector and method for locating electrical power supply noise sources

ABSTRACT

A procedure is described for locating the source of electrical noise generated in any branch of an electrical power distribution network. A noise probe, consisting of a small coil mounted in an insulated housing which is held near a power supply line to inductively couple to the magnetic field of the noise current present in that line, is employed to find the source of electrical noise.

United States Patent 1191 Gunn et al. Aug. 14, 1973 [541 ELECTRONICSWITCHING TRANSIENT 689,253 12/1901 DETECTOR AND METHOD FOR LOCATING27751736 12/1956 1 2,789,268 4/1957 Bechtel et al 324/66 ELECTRICALPOWER SUPPLY NOISE 1,344,388 6/1920 Eisenmann 324/133 SOURCES [75]Inventors: John B. Gunn, Mount Kisco; John L.

Staples, Pleasantville, both of NY. Primary Examiner-Gerard R. Strecker[73] Assignee: International Business Machines Attorney-George BaronCorporation, Armonk, N.Y. 221 Filed: Dec. 6, 1971 57 BSTRACT A [2]]Appl. NO.: 204,881 1 A procedure is described for locating the source of[52] [1.8. CI. 324/52, 324/127, 324/ l 33 electrical noise generated inany branch of an electrical [51] Int. Cl. G01r 19/14, GOlr 31/08 powerdistribution network. A noise probe, consisting [58] Field of Search324/52, 66, 67, 103, of a small coil mounted in an insulated housingwhich 324/127, 133 is held near a power supply line to inductivelycouple to the magnetic field of the noise current present in that [56]References Cited line, is employed to find the source of electricalnoise.

UNITED STATES PATENTS 2,808,566 10/1957 Douma 324/127 4 Claims, 5Drawing Figures I" 8 EXTERNAL x l d TRIGGER f 54 48 INl UT 10x m j p IATTEN. 40 ATTEN.

PAIENTED All: I 4 I913 SHEI 1 OF 3 FIG.1

EXTERNAL- TRIGGER INPUT FlG.2

INVENTORS JOHN B. GUNN JOHN L. STAPLES ATTORNEY mm 14 ms LOAD NOISESOURCE POINTING TOWARD NOISE SOURCE snmanrs FIG. 5

POWER SUBSTATION i (t) M power ELECTRONIC SWITCHING TRANSIENT DETECTORAND METHOD FOR LOCATING ELECTRICAL POWER SUPPLY NOISE SOURCES BACKGROUNDOF THE INVENTION This invention relates to apparatus and a method ofusing such apparatus so as to enable one to locate the source ofelectrical noise generated within a power substation distribution systemand power lines being fed by such substation. Power line noise is asource of trouble in areas, such as a research laboratory or at anylocation, where sensitive electrical measurements are being made. Mostknown prior techniques for establishing a noise-free environment aretime consuming and te dious, particularly when several noise sources maybe operating simultaneously. The present invention relies upon a simpleyet direct and efficient way of detecting each source of generated noisethat comprises a coil mounted in an insulated housing. The coil isinductively coupled to the magnetic field of the noise current presentin a conductor and such coil is designed to eliminate electrostaticcoupling and minimize 60. cycle in ductive coupling. The coil housingismarkedor has an arrow affixed to it to indicate the current sense forapositive electromotive force induced by thenoise pulse in the coil. Thedirection in the conductor from which the noise is coming is determinedby comparing the sense of the current pulses in the conductor with thesense of the corresponding voltage pulses. When the polarity of thevoltage pulse on the conductor is the same as that induced in the coilby the noise current in the conductor, the arrow on the housing has beenchosen to be pointing toward the source of line noise. By judiciouslychoosing measuring points along-a noisecarrying line, the choice beingbased on the direction noted in the previous readings, the source ofinterfering noise can be quickly located. After such location,corrective measures, such as the use of electrical filters at theoffending noise source, will prevent future propagation of noise fromthe source back into thepower distribution system.

It is an object of this invention to provide a simple but effectivemeans for pinpointing the source of electrical noise being generated ata power substation or in any line emanating from that power substation.

It is another object to provide a directiomfinding noiseprobe andassociated electronic circuitry that is readily portable.

it is a further object to provide a portable directionfmding noisedetector probe in conductors havinghigh noise levels.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic representation oftheinvention showing the probe and its associated electronic circuitry.

FIG. 2 is a cross-sectional view of the probe itself and its housing inoperation as a test device.

FIG. 3 is a perspective view of the probe and housing used in FIGS. 1and 2. i

FIG. 4 is a schematic diagram of a flow diagram illustrating noisepulses on power lines and how the invention is used to detect them.

FIG. 5 is a schematic showing of the manner in which the arrow on theprobe housing is made to point in the direction of the noise source.

DESCRIPTION OF THE PREFERRED EMBODIMENT in FIG. 2 is shown the basicprobe 2 encased in and supported by an insulating housing 4. Probe 2includes a small coil 6 mounted in an electrostatically shieldedcompartment C in the insulated housing 4 so that the coil, when placednear aconductor, is inductively coupled to the magnetic field of anynoise current present in that conductor, and a voltage pickup lead 8which is in electrical contact with theconductor for sensing thepolarity of the noise voltage on the conductor. The housing 4 is markedwith an arrow 10 which is used in determining the direction of the noisesource. In this illustration, the arrow will be pointing either into theplane of the drawing or out of the plane of the drawing. That is, theinitial orientation of coil 6 and the manner in which it is connected toan oscilloscope, to be discussed hereinafter, are such that when apositive noise voltage polarity sensed by voltage pickup lead 8 isaccompanied by apositive current sense output, then the arrow 10 ispointingtoward the noisesource, and when a positive noise voltage isaccompanied by a negative current output, then the arrow TOis pointingaway from the noise source.

Before describing the circuitry employed in determining noise sources inaconductor, attention is drawn to FIG. 2 wherein an example of a threephase power bus duct 12 is shown. The duct 12 issgrounded and has threeconductors l4, l6 and 18 carrying the different phase currents o d, anddi with the fourth conductor 20 being neutral. To take a reading ofsuspected noise currents on a line, terminal is grounded to the busduct, the insulated housing 4 rests on one of the openings in bus duct12, in proximity to a power conductor, such as conductor 16, withvoltage pickup probe lead 8 contacting the conductor 16 and the coil '6being under the magnetic influence of noise currents flowing throughthat conductor. The one using the probe 2 has the arrow 10 in his viewwhile the test is being made.

Attention is directed to FIG. 1 to illustrate the manner in which anactual noise detection test is made. The enclosure C serves as anelectrostatic shieldgshown as a dotted rectangle, in which is carriedthe coil 6. Resistor 22 is in electrical parallel with coil 6 andresistor 24 is in series with coil 6. One end ofcoil 6 is groundedthrough shielded cable 26 and theother end of said coil terminatesthrough resistor 24 atone of the terminals 28 of switch 30.

The voltage pickup lead 8 connects "to ground, through fuse 32 and twoparallel R-C networks, the first consisting of capacitor 34 and resistor36 and the second consisting of resistor 38 and capacitor 40. Anatte'nuator circuit 42 connects the voltage picked up by lead 8 anddifferentiated by capacitor 34 and resistor 36 through terminal 44 andswitch 30 to the vertical input (VI) of a portable oscilloscope. Theparticular scope used in implementing the invention is the Sony-Tektronix 323. A second attenuator circuit 48 is connected from thesecond R-C "circui'tr'to the external trigger input terminal ofoscilloscope Coil 6 has an inductance of 50 millihenries, resistor 22has a resistance of a thousand ohms and resistor 24 a resistance of2,000 ohms so that the noise induced current in such coil masks thecurrent induced by the 60 cycle wave from the power line. Resistors 22and 24 serve as damping resistors and coil 6 and resistor 22 form a highpass filter suppressing the 60 cycle current signals on the line beingprobed. In a similar manner; capacitor 34 has a value of 0.02 Mfd andresistor 36 has a resistance of 1,000 ohms so that such R-C circuit actsas a high pass filter or differentiator allowing only the noise voltageto be transmitted to the oscilloscope and suppressing the normal 60cycle power line voltage. This circuitry thus emphasizes the spikes,i.e., line noise, sensed by voltage pickup lead 8 and diminishes thenormal sine wave signals on the line. In a similar manner, resistor 38has a value of 10,000 ohms and capacitor 40 a value of 0.1 [.Lfd so thatthe combined R-C circuit is a filter of high frequency noise pulses butallows the 60 cycle sine wave from the power line to pass throughattenuator circuit 48 to the external trigger input of oscilloscope 46.This trigger network provides a smoothed 60 cycle sine wave from thepower line which allows triggering of the time base of the oscilloscope46 to display noise pulses on an expanded time scale over most of thepower line cycle. The balance of the power line cycle may be studiedusing the horizontal position control of the oscilloscope.

Thus when probe 2 is inserted in a power line, as seen in FIG. 2, thecircuit of FIG. 1 can be made to alternately display the polarity of thenoise voltage v, and the polarity of the noise current i,, by switchingthe arm of switch back and forth from terminal 44 to terminal 28. Theoscilloscope 46 will alternately display the polarity of the v, and i,,on its screen. The probe has been calibrated so that if both suchpolarities are the same, then the arrow 10 on housing 4 is pointingtowards the noise source. If the polarities are of opposite sense, thenthe housing 4 in which the probe is housed in rotated 180 so that thepolarities match and arrow 10 is again pointing toward the source ofnoise on the line.

FIG. 5 illustrates how such a calibration is carried out. A substationdelivers power along a conductor 18 to a load, and it is assumed thatthe latter is a source of electrical noise which travels as noise pulsei,,(t) from the load back toward the substation. Voltage probe 8 sensesthis noise as 1 ,,(1). The noise current i,, generates a magnetic fieldM around conductor 18 so that such field M is coupled to coil 6, thelatter being wound so that such noise current i, induces a positivevoltage v[i(t)] at the left terminal of coil 6. Fixed arrow 10 on thehousing 4 is marked to point toward the direction of the noise sourcewhen v,,(t) has the same polarity as u[i,,(t)]. Obviously, thecalibration could be turned around so that when the polarity of 1 ,,(2)is opposite to that of v[i,,(t)], the fixed arrow 10 points toward thesource of noise without departing from the spirit of the invention.

FIG. 4 is a schematic representation of the manner in which the testprobe is used to pinpoint the location of noise in a network ofconductors feeding power to various loads. Assume that box 50 representsa power substation, lines 52, 54, and 56, etc. represent various powerbus ducts 12 and boxes L L L represent many loads, such as laboratoriesand testing stations employing many electronic devices, some of thelatter acting as generators of noise pulses which propagate in bothdirections along the power bus to which the equipment is electricallyconnected. Thus, if station L. is generating noise, such noise willpropagate above and below line 56 away from point P and affect all otherstations.

Assume that Test Point No. l is chosen on a power line suspected ofcarrying noise pulses. The housing 4 of the probe 2 is inserted at anaccess port in the power bus duct (See FIG. 3) and switch 30 (SeeFIG. 1) is switched back and forth between terminals 28 and 44 to obtaina reading of a noise pulse v, and, if such exists, its correspondingcurrent pulse i... If the polarities of 11,, and i are of the samesence, as indicated in FIG. 4, then the fixed arrow 10 on the insulatedhousing 4 is pointing toward (to the right) the source of noise on line52. If these polarities are of an opposite sense, then the housing a isrotated to indicate that the source of noise is somewhere to the left oftest point No. 1.

The probe 2 is moved to the right along duct 52, until point P, isreached, the latter point being the junction of three ducts 52, 54, and56. The testing may continue either along duct 54 or 56. In the instantcase, the probing continued along duct 54, and v, and i, were constantlymonitored by oscilloscope 46. Soon after point P, was passed, the senseof polarity of i was negative and that of 11,, was positive.Consequently, arrow 10 on housing 4 was pointing away from the noisesource, and the noise source must be located along bus duct 56. Testsare continued along bus duct 56 until the change in polarity of i,,between test point No. 3 and test point No. 4 indicates the source ofnoise as being located in station L By study of the nature of theequipment used at location I... and the type of noise spikes beinggenerated, corrective measures can be taken to eliminate the cause ofnoise. For example, by selectively switching off individual suspectedpieces of equipment at location L. and continuing to monitor the noiseor its absence from location 1. the specific source of noise can beisolated. Appropriate measures, such as the use of filters, shieldsreplacement of parts of the offending equipment, etc. may be resorted toso as to attenuate or eliminate the noise, but such measures are notpart of the instant invention and will not be discussed herein.

This invention is particularly useful when the noise pulses occur in adefinite pattern, frequently betraying the fact that a particular typeof equipment is responsible for the noise spikes. In general, as happensoften when many substations are used, each power line phase from aparticular substation has a different pattern of pulses which propagatesthroughout the distribution system with little change in amplitude, orsuch definite pattern appears which is characteristic of particularequipment. This information, when added to the information obtained bythe method of this invention, can greatly reduce the time needed forlocating noise sources in a complex electrical network.

The invention, while described as a means of detecting repetitive noisespikes, is not so restricted. The thrust of the contribution lies incomparing the polarity sense of the noise voltage pulses with thepolarity sense of current induced voltage in coil 6 by such noisepulses, with the arrow 10 on housing 4 determining the direction ofnoise source. If the noise spikes are transient, and random. then amemory unit can be employed in conjunction with this invention to retainthe polarity sense of that transient and random pulse. Changes in i,,with respect to 1/, can be observed in this memory unit and theprocedure for locating the noise source is the same as that forrepetitive pulses.

This invention is particularly helpful where a given substation suppliesmany locations, for example, about 100 or more laboratories situated ondifferent floors. Unless a relatively simple and reliable method isrelied upon to trace the origin of a noise-generating electrical source,the time consumed would be enormous. The novel method described hereinis a quick and direct technique for locating the direction in which anoise pulse is traveling through a power system and permits one topinpoint, by using a few judiciously chosen test points, the exactlocation of the ofiending noise generator.

What is claimed is:

1. A direction finding noise probe for locating the source of electricalnoise in an electrical network having a plurality of branch circuitscomprising an insulated housing having a fixed arrow marking on saidhousing,

a voltage pickup probe on said housing for coupling directly to saidnoise voltage at a selected point in said network so as to produce areference noise voltage polarity,

an electromagnetic coil within said housing inductively coupled to themagnetic field of the noise pulse current present in said network atsaid selected point in the network so as to induce a voltage polarity ofsaid noise current pulse in said coil, means for sensing said referencevoltage polarity,

means for sensing the polarity of said induced noise current pulse, and

means for comparing said two polarities whereby said fixed arrow pointsin the direction of noise source in said network when said polaritiesare equal and away from said noise source when said polarities areunequal.

2. A direction-finding noise probe for locating the source of electricalnoise in an electrical network having a plurality of branch circuitscomprising an insulated housing having a fixed arrow marking thereon,

an electromagnetic coil within said housing for being inductivelycoupled to the magnetic field created by a noise current pulse presentin a conductor of one of said branch circuits so as to produce a noisevoltage pulse of a given polarity in said coil;

means for sensing the polarity of said noise-induced voltage in saidcoil,

a voltage pickup lead on said housing for sensing the voltage polarityof said electrical noise pulse, and

means for displaying said two polarities whereby said fixed arrow pointsin the direction of origin of said noise pulse in said conductor whensaid polarities are equal and away from the origin of said noise pulsewhen said polarities are unequal.

3. A direction-finding noise probe for locating the source of electricalnoise in an electrical network having a plurality of branch circuitscomprising an insulated housing having a fixed direction-pointing markerthereon,

a voltage pickup probe on said housing for coupling directly to saidnoise voltage at a selected point in said network so as to produce areference voltage polarity,

an electromagnetic coil within said housing inductively coupled to themagnetic field of the noise pulse current present in said network atsaid selected point in the network so as to induce a voltage polarity ofsaid noise current pulse in said coil,

means for sensing both the polarity of said reference voltage and saidinduced noise current pulse,

an oscilloscope, having a triggering circuit, for displaying said twopolarities on its screen, and

a differentiating network connected between said voltage probe and saidtriggering circuit so that the noise voltage pulse is emphasized and thenormal sine wave voltage on said conductor is diminished in the displayof said polarities.

4. In a method for detecting the source of electrical noise in anelectrical network having a plurality of branch circuits comprising thesteps of:

a. simultaneously sensing the current and voltage of that electricalnoise on a given branch circuit, wherein similar polarities of the noisevoltage and noise current indicate that the source of noise is comingfrom a given direction,

b. continuing sensing said noise pulse in said branch circuit, whilemoving said probe in said given direction, until the polarity of thenoise current pulse reverses with respect to the polarity of the noisevoltage pulse, said reversal of polarity indicating a first branchcircuit that is a source of electrical noise,

0. continuing sensing said noise pulse along said first branch circuituntil the polarity of the induced noise current pulse is opposite to thepolarity of the induced noise voltage pulse so as to locate a secondbranch circuit that is a source of electrical noise, and

d. continuing similar sensing of the noise pulse until a final circuit,having no further branches associated therewith, is located as thegenerator of such electrical noise.

w k a

1. A direction-finding noise probe for locating the source of electricalnoise in an electrical network having a plurality of branch circuitscomprising an insulated housing having a fixed arrow marking on saidhousing, a voltage pickup probe on said housing for coupling directly tosaid noise voltage at a selected point in said network so as to producea reference noise voltage polarity, an electromagnetic coil within saidhousing inductively coupled to the magnetic field of the noise pulsecurrent present in said network at said selected point in the network soas to induce a voltage polarity of said noise current pulse in saidcoil, means for sensing said reference voltage polarity, means forsensing the polarity of said induced noise current pulse, and means forcomparing said two polarities whereby said fixed arrow points in thedirection of noise source in said network when said polarities are equaland away from said noise source when said polarities are unequal.
 2. Adirection-finding noise probe for locating the source of electricalnoise in an electrical network having a plurality of branch circuitscomprising an insulated housing having a fixed arrow marking thereon, anelectromagnetic coil within said housing for being inductively coupledto the magnetic field created by a noise current pulse present in aconductor of one of said branch circuits so as to produce a noisevoltage pulse of a given polarity in said coil; means for sensing thepolarity of said noise-induced voltage in said coil, a voltage pickuplead on said housing for sensing the voltage polarity of said electricalnoise pulse, and means for displaying said two polarities whereby saidfixed arrow points in the direction of origin of said noise pulse insaid conductor when said polarities are equal and away from the originof said noise pulse when said polarities are unequal.
 3. Adirection-finding noise probe for locating the source of electricalnoise in an electrical network having a plurality of branch circuitscomprising an insulated housing having a fixed direction-pointing markerthereon, a voltage pickup probe on said housing for coupling directly tosaid noise voltage at a selected point in said network so as to producea reference voltage polarity, an electromagnetic coil within saidhousing inductively coupled to the magnetic field of the noise pulsecurrent present in said network at said selected point in the network soas to induce a voltage polarity of said noise current pulse in saidcoil, means for sensing both the polarity of said reference voltage andsaid induced noise current pulse, an oscilloscope, having a triggeringcircuit, for displaying said two polarities on its screen, and adifferentiating network connected between said voltage probe and saidtriggering circuit so that the noise voltage pulse is emphasized and thenormal sine wave voltage on said conductor is diminished in the displayof said polarities.
 4. In a method for detecting the source ofelectrical noise in an electrical network having a plurality of branchcircuits comprising the steps of: a. simultaneously sensing the currentand voltage of that electrical noise on a given branch circuit, whereinsimilar polarities of the noise voltage and noise current indicate thatthe source of noise is coming from a given direction, b. continuingsensing said noise pulse in said branch circuit, while moving said probein said given direction, until the polarity of the noise current pulsereverses with respect to the polarity of the noise voltage pulse, saidreversal of polarity indicating a first branch circuit that is a sourceof electrical noise, c. continuing sensing said noise pulse along saidfirst branch circuit until the polarity of the induced noise currentpulse is opposite to the polarity of the induced noise voltage pulse soas to locate a second branch circuit that is a source of electricalnoise, and d. continuing similar sensing of the noise pulse until afinal circuit, having no further branches associated therewith, islocated as the generator of such electrical noise.